There are lifeboat launching appliances from offshore installations, wherein the lifeboat can be launched as a free fall lifeboat or wherein the lifeboat can be launched by falls. The free fall lifeboat launching from an oil rig usually means that the lifeboat is stored on a tilted ramp and can be slid through the ramp into the water under its own weight if a holdback is released. The lifeboat can be recovered usually by a hydraulic davit and a spreader of a wire rope winch. The lifeboat may be attached to spreader chains by two pairs of slings. The lifeboat launching from an oil rig by falling under gravity usually means that the lifeboat is stored above sea level and can be lowered into the water by fall of a winch under its own weight if a brake of the winch is released. The lifeboat can be recovered by the opposite operation of the same wire rope winch.
A disadvantage of the present lifeboat launching systems from an oil rig is that in the case of the emergency situation and while the power supply is off, the lifeboat of one lifeboat launching system can be launched as only a free fall lifeboat or as only a conventional lifeboat by falls. Due to an obligation to ensure that people can abandon the oil rig safely with the use of the lifeboat in any circumstances whatsoever, in the event of a life threat, an oil rig may have both of these two different lifeboat launching systems. Such duplicate systems, however, increases the cost of the system and the cost of its service.
Although being the most effective, a disadvantage of the present free fall lifeboat launching system from an oil rig is that the free fall lifeboat launching system is not safe in certain circumstances. An example of such circumstances is the need to abandon an oil rig by the free fall lifeboat while the sea is covered by ice or the wreckage of the oil rig damaged by explosion and the like, wherein the risk of damage or breakdown of the lifeboat is high, particularly while visibility is reduced or when at night. The evacuation of injured people whose transport requires immobilization also should not be carried out by the free fall lifeboat if another, more appropriate, solution may exists. A disadvantage of the present lifeboat launching by gravity by falling from the oil rig is that, for some circumstances such as a high sea, if the lifeboat release mechanism malfunctions, manual disengagement may not be safe or even feasible.
A common disadvantage of both lifeboat launching systems is that usually the lifeboat launching arrangement is located on the open deck of oil rig. This location may reduce the safe abandonment of the oil rig during bad weather, fire and explosion, and, due to the direct exposure to the weather conditions, may cause a reduction in the efficiency of system operation and may increase the cost of service. Moreover during winter time, the freezing weather or snow may be the cause of the unsuitability of the lifeboat launching appliance for immediate use. Likewise, marine environment pollution may result as a result of wire ropes and moveable part bearings greasing.